Reducing the influence of non-target stimuli on saccade accuracy: predictability and latency effects

When the eye saccades to a group of eccentric targets, it tends to land in a position which can be loosely described as the center of gravity of the configuration. By using letter targets within strings of letters, it was shown in two experiments that this "global effect", that is, the influence of the non-target elements on saccade accuracy, can be attenuated when the "where" calculation is facilitated or when the moment of saccade triggering is sufficiently delayed. Arguments are given in order to show that the improvement of saccade accuracy observed is a perceptual and not a motor effect and, some hypotheses are then presented for a possible underlying mechanism. It is also suggested that the exact position where the eye lands can be calculated from a linear combination of two tendencies: a tendency to saccade to the aimed-for target, and a tendency to saccade to a "gaze attraction position". Closer consideration showed that this gaze attraction position is not exactly at the center of gravity of the configuration, but less eccentric than it, possibly due to weighting by a cortical magnification factor.